1. Field of the Industrial Application
This invention relates to a starter motor with an intermediate gear (hereinafter referred to as "an intermediate gear type starter motor", when applicable) the rotation of which is transmitted through the overrunning clutch and the intermediate gear to the ring gear of an engine, thereby to start the latter.
2. Description of the Prior Art
FIG. 1 is a sectional view showing essential components of a conventional intermediate gear type starter motor which has been disclosed, for instance, by Japanese Utility Model Application (OPI) No. 84369/1983 (the term "OPI" as used herein means an "unexamined published application"). In FIG. 1, reference numeral 1 designates a DC motor, in which an armature rotary shaft 3 is extended forwardly (to the right in FIG. 1) from its armature 2; and 5, a front bracket to which the DC motor 1 is coupled, the front bracket 5 supporting the front end portion of the rotary shaft 3 through a sleeve bearing 6.
Further in FIG. 1, reference numeral 7 designates an overrunning clutch which is slidably mounted on the rotary shaft 3. The overrunning clutch 7 is designed as follows: Reference numeral 8 designates a clutch outer which is engaged with the helical spline gear 4 formed on the rotary shaft 3 so as to be rotated thereby. Reference numeral 9 designates a clutch inner which transmits rotation through rollers 10 to the clutch outer 8 in one way. The clutch inner 9 is mounted on the rotary shaft 3 through a sleeve bearing 17. A pinion 11 is formed in the front end portion, of the clutch inner 9. Reference numeral 12 designates a clutch cover which is secured through a stiffening plate 12 to the clutch outer 8 by staking; 14, a locking ring secured to the clutch outer 8, thus defining an engaging groove 15 with a step of the clutch outer 8; and 16, an eccentricity regulating ring secured to the inner cylindrical wall of the clutch outer.
Further in FIG. 1, reference numeral 20 designates a shift lever which has a forked end portion engaged with the engaging groove 15, and an fulcrum portion at the middle which is supported by a supporting plate 21. The supporting plate 21 is supported through a cushioning spring 23 on a grommet 22 secured to the yoke of the motor 1. The other end portion of the shift lever 20 is coupled to the end portion of the plunger (not shown) of an electromagnetic switch mounted on the motor 1, so that the shift lever 20 is turned about its fulcrum portion.
Reference numeral 24 denotes a supporting shaft fixedly secured to the front bracket 5 in such a manner that shaft 24 is in parallel with the rotary shaft 3; 26, designates an intermediate gear mounted on the supporting shaft 24 through a sleeve bearing 28 secured to the inner cylindrical wall of the intermediate gear, the intermediate gear 26 having a boss 26a in the outer cylindrical wall of which an annular groove 27 is formed; and 29, a shift ring secured to the outer cylindrical wall of the clutch cover 12. The shift ring 29 has an annular protrusion (flange) 29a radially extended, which is engaged with the annular groove 27.
The annular protrusion 29a of the shift ring 29 is engaged with the annular groove 27 of the intermediate gear 26 as shown in FIG. 2.
The operation of the conventional starter motor thus constructed will be described.
When the exciting coil of the electromagnetic switch (not shown) is energized, the plunger is attracted so as to turn the shift lever 20 counterclockwise. As a result, the overrunning clutch 7 is moved forwardly (in the direction of the arrow A) until it strikes against a stopper 18 provided on the rotary shaft. As the overrunning clutch 7 is moved in this way, the intermediate gear 26 is moved on the supporting shaft 24 with the aid of the shift ring 29, thus engaging with the ring gear 30 of the internal combustion engine. Thereafter, the stationary contact means in the electromagnetic switch is closed, so that current flows in the circuit of the DC motor, whereby the armature 2 is rotated, and the rotation of the rotary shaft 3 is transmitted through the overrunning clutch 7, the pinion 11 and the intermediate gear 16 to the ring gear of the internal combustion engine, to start the latter.
In the conventional starter motor described above, the engagement, in the axial direction, of the annular protrusion 29a of the shift ring 29 with the annular groove 27 of the intermediate gear 26 is limited in width; that is, the engagement is effected only in the upper portion of the annular groove 27. Hence, when the overrunning clutch is moved, the moment acts on the intermediate gear, thus obstructing the smooth axial movement of the intermediate gear. Furthermore, since the engagement area of the annular protrusion 29a and the annular groove 27 is small, the force of movement is not positively transmitted, and therefore the annular protrusion 29a and the annular groove 27 are liable to be worn greatly, thus shortening the service life.